Insoluble anodes



United States Patent 3,007,856 INSOLUBLE AN ODES Burton Bower Knapp, Westfield, and Waclaw Andrew Wesley, Plainfield, N.J., assiguors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 6, 1960, Ser. No. 686 5 Claims. (Cl. 204-49) The present invention relates to insoluble anodes and, more particularly, to special nickel anodes for use as insoluble anodes in electroplating solutions, e.g., sulfatetype nickel plating solutions.

It is well known in the art of electroplating that insoluble anodes are of significant industrial and commercial importance in many diversified applications. For example, insoluble anodes are commonly utilized in electroplating processes involving coating of the inner surfaces of pipes and tubes, plating of rolls, strip or wire at high current densities, electroforming of complicated shapes, etc. Advantages of using insoluble anodes in such processes include elimination of anode bags, reduction of anode scrap losses and elimination of addition agents used to prevent pitting. Moreover, evolution of gas at the insoluble anode provides an agitative action whereby high anode and cathode current densities are more readily achieved In addition thereto, the relatively permanent shape of insoluble anodes is conducive to or permissive of a close and unchanging anode-to-cathode spacing. This factor is of primary importance in such applications as continuous strip plating, plating the inside of tubes, and electroformmg.

Heretofore, the art has employed insoluble anodes comprised of lead invarious plating baths, including nickel plating baths. In nickel plating baths, e.g., allsulfate nickel plating baths, experience has shown that lead not only contaminates the plating solution but also co-deposits with the nickel, thereby forming an impure deposit. When such a deposit is subsequently heated or Welded, the lead content thereof causes deleterious emhrittlemeut. In attempts to overcome the disadvantages of lead insoluble anodes it has been proposed to utilize wrought nickel, e.g., commercially purse wrought nickel, such as is sold under the trademark A nickel, the properties of which are set forth in the Metals Handbook, 1948 ed., page 1047, as an insoluble anode in nickel plating solutions, e.g., sulfate-type nickel plating baths. The wrought nickel insoluble anode, while it substantially obviated the disadvantages of the lead insoluble anode, has been found to possess serious attendant difficulties. For example, such insoluble anodes generally exhibit an undesirably high anode current efliciency, e.g., to percent or higher, depending upon the condition of the electrolyte. Moreover, some bath impurities tend to increase the corrosion rate of wrought nickel insoluble anodes. In allsulfate type nickel plating baths the corrosive attack on prior art wrought nickel insoluble anodes is intergranular in nature and, as aconsequence thereof, loose grains of nickel slough off the anode causing the formation of rough deposits at the cathode. Although attempts were made to overcome the foregoing difiiculties and other difliculties, none, as; far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that a new composite anode can be used as an insoluble anode in electroplating solutions, particularly sulfate-type electroplating solutions, with highly satisfactory results with respect to the attainment of low anode current efficiencies and the avoidance of deleterious intergranular corrosive attack.

It is an object of the present invention to provide an anode for use as an insoluble baths.

Another object of the invention is to provide a new insoluble anode capable of exhibiting a relatively low anode current efliciency in electroplating solutions of the sulfate type, for example, all-sulfate nickel plating solutions.

The invention also contemplates providing a new insoluble anode for use in electroplating solutions of the sulfate type and particularly nickel sulfate-containing solutions which, during corrosive attack, will not, to any appreciable or detrimental extent, cause the formation of rough deposits at a cathode.

It is a further object of the invention to provide a new insoluble anode characterized in that it can be formed to any desired configuration.

The invention further contemplates providing a process for accomplishing the foregoing objects.

Generally speaking, the present invention contemplates the provision of an improved composite insoluble anode for use in plating processes and having a duplex structure. The composite insoluble anodes contemplated in accordance with the invention are comprised of a foundation metal or alloy, preferably in wrought form, having superimposed thereon an adherent surface layer of electrodeposited nickel. Foundation metals or alloys which can be satisfactorily used include nickel, low-carbon nickel, iron, copper, aluminum, Zinc, tin, antimony, bismuth, alloys of the foregoing including those comprised of nickel-copper, iron-nickel, copper-nickel, tin-zinc, tin-bismuth, tin-lead, antimony-bismuth, bismuth-tin, zinc-aluminum, zinc-tin. Nickel alloys such as sold under the trademarks D Nickel, Duranickel and Permanickel are also contemplated as satisfactory foundation materials. In accordance With the present invention, our insoluble anodes are adapted for use in substantially halide-free nickel plating baths, e.g., all-sulfate nickel plating baths or nickel sulfamate baths. When employed in such baths, the insoluble anodes of the present invention exhibit a very desirable low anode current efliciency, for example, 6% or 5%. Moreover, during corrosive attack our nickel-plated composite insoluble anodes are not subject to intergnanular attack to any appreciable or detrimental extent. Thus, relatively smooth cathode deposits are assured since no interference is incurred through formation of loose nickel particles or grain.

In carrying the invention into practice, it is important that the anode current density be controlled and maintained such that it does not fall below about 30 amperes per square foot (a.s.f.) and preferably not below about 40 a.s.f. In achieving highly satisfactory results, it is preferred that an anode current density of 50 to a.s.f. be maintained although current densities of a.s.f. or higher can be employed without detrimental results. Low anode current densities, e.g., 5 a.s.f., result in high anode current efliciencies and accompanying deleterious c0r rosion of the anode. The pH of the plating bath should be not less than pH 1 and not greater than pH 4.5. It is preferred, for best results, to maintain the pH of the electrolyte between pH 1.5 and pH 3.5. The temperature of the bath should be maintained between the temperatures F. and 160 F. and it is preferred to maintain the temperature between F. and F. With temperatures below 120 F. the rate of plating is slower than when higher temperatures are employed. This would be commercially undesirable.

Further, it is preferred to employ wrought nickel as the foundation metal for the nickel-plated anode, particularly in all-sulfate nickel electroplating solutions. This feature advantageously obviates danger of contamination of the plating bath if the nickel electrodeposit is accidentally perforated during service. Furthermore, wrought nickel advantageously permits obtaining insoluanode in electroplating ble anodes of desired shape or configuration and provides a suitable basis upon which the surface of electrodeposited nickel can be renewed when required. It is also a preferred feature of our invention that the thicknesses of the electrodeposit be not less than about 0.005 inch and not more than about 0.1 inch. It is preferred that the thickness of electrodeposit be about 0.01 inch to about 0.05 inch.

The composite insoluble anodes of the present invention are characterized by a duplex structure comprised of an electrodeposit of nickel having a columnar microstructure and a foundation metal of non-columnar microstructure.

For the purpose of giving those skilled in the art a better appreciation of the advantages of the invention, the following illustrative examples are set forth hereinbelow:

Example I An eight-inch section of a rolled carbon nickel bar 4 inch in diameter was subjected to a pre-treatment operation involving the steps of (l) degreasing the surface thereof, (2) cathodically cleaning the bar in a hot alkaline cleaner followed by a rinsing action, (3) treating the bar first anodically in a cold solution of H 50 while using a current density of about 20 a.s.'f. (amperes per square foot) for about 10 minute and then for 2 minutes at a current density of about 200 a.s.f. and then treating the bar cathodically for about 2 to 3 seconds at a current density of 200 a.s.f. and, (4) subjecting the bar to a final rinse. Employing a conventional Watts-type nickel plating bath and using plating conditions well known by those skilled in the art, a nickel electrodeposit of about 0.05 inch was then deposited upon the bar. The nickel-plated composite bar so obtained was then employed as an insoluble anode in nickel plating the inside of a pipe approximately 8 inches in length and having an inside diameter of about 1% inches. The plating bath employed was of the all-sulfate nickel type and contained about 300 g.p.l. (grams per liter) of NiSO .7H O and about g.p.l. of H BO The temperature of the plating bath was maintained at about 130 F. and the pH thereof was 1.5 to 2 during the plating operation. The plating operation was conducted using a current density of about 75 a.s.-f. for about 33 ampere-hours after which the plating operation was discontinued. It was found upon analysis that the weight loss of the nickel-plated composite bar used as the insoluble anode was only about 2 grams, which in terms of anode current efficiency is about 5%. No loose nickel grains or particles were observed and the inside of the pipe was characterized by a smooth nickel electrodeposit.

Example II A cold drawn core of A nickel approximately 6% inches in length and about 0.82 inch in diameter was subjected to the same general pre-treating and Watts-type plating operations as described in connection with Example I except that the plating operation was discontinued when the nickel electrodeposit was about 0.01 inch in thickness. The composite anode so formed was then employed as the insoluble anode in a sulfate electroplating solution of the same composition set forth in Example I and, under the same plating conditions described in conjunction therewith, two nickel sheets of about 8 inches in length and 10 inches in width were used as cathodes for plating purposes. The plating operation was discontinued after about 47 ampere-hours. An analysis of the nickel-plated composite insoluble anode showed that the weight loss thereof was approximately 2 grams which, when calculated in terms of anode current efliciency, is about 4%. Again, no loose nickel grains or particles were detected and the cathode electrodeposits were smooth.

It is to be observed that the present invention provides for a markedly improved insoluble anode capable of eX- hibiting low anode current efliciencies when employed in electrodeposition processes. The present invention as described herein affords a new and markedly improved nickelplated composite insoluble anode capable of manifesting low anode current efiiciencies of about 6% to 5% or lower in electroplating procedures and particularly those where all-sulfate nickel plating baths are employed. In addition thereto, the insoluble anodes contemplated within the scope of the present invention do not interfere with the deposition of smooth cathode deposits.'

Furthermore, the invention provides for a substantial improvement in nickel electroplating procedures utilizing insoluble anodes. It will be noted that since the insoluble anodes of the present invention operate at very low anode current efficiencies in electrolytes, such as the all-sulfate nickel type, replenishment of the electrodeposited surface thereof is substantially reduced, thereby providing for a convenient electroplating procedure without frequent changing of the anodes. Moreover, deleterious electrolyte contamination is obviated in accordance with the present invention. In addition, the insoluble anodes of the present invention, being of a composite structure as aforedescribed, can be readily used even in processes involving the plating of complicated shapes. Such processes necessitate the use of insoluble anodes of permanent shape to insure, for example, proper anode-to-cathode spacing. Because the core metal, e.g., nickel, of the insoluble anodes contemplated within the invention is of wrought form, a predetermined and desired anode shape can be easily obtained by standard working procedures.

It is to be noted that the present invention is not to be confused with non-composite nickel insoluble anodes used heretofore. Such prior art insoluble anodes are disadvantageous from the viewpoint of intergranular corrosive attack and the comparatively high anode current efiiciencies associated therewith.

Whenever the expression all-sulfate electroplating solution or bath has been used herein or in the appended claims it is to be understood, as will be apparent to those skilled in the art, as meaning a plating bath whose principal anion, other than that associated with the buffering agent if any, is the sulfate ion and which is substantially devoid of halide ions, i.e., the halide ion concentration, e.g., chloride ion concentration, is less than 1.5 grams per liter.

The term wrought nickel as employed hereinbefore and in the appended claims is intended to include, as will be readily recognized by the skilled artisan, commercial wrought forms of nickel which respond readily to all commercial fabrication processes. A typical composition is 99.4% nickel, 0.1% copper, 0.15% iron, 0.25% manganese, 0.05% silicon, 0.05% carbon and 0.005% sulfur.

The present application is a continuation-in-part of our copending patent application Serial No. 641,236, filed February 20, 1957, and since abandoned.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. For example, foundation metal in cast form can be employed. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A new and improved insoluble anode nickel electroplating method for providing low anode current efiiciencies of not greater than about 6% and for preventing detrimental intergranular corrosion of the anode which comprises, establishing an all-sulfate nickel plating solution in contact with a cathode and an insoluble anode characterized by a composite structure comprised of a core of wrought nickel and a firmly adherent surface layer of electrodeposited .nickel, maintaining the anode current density such that it does not fall below about 30 a.s.f., and controlling the pH of said plating solution at a pH of not less than about 1 and not greater than about 4.5 while maintaining the temperature of said plating solution at a temperature of not less than about 120 F., whereby a smooth cathode deposit of nickel is obtained.

2. A method as described in claim 1 wherein the current density is maintained in the range of 50 a.s.f. to 80 a.s.f.

3. A method as described in claim 1 wherein the pH is not less than pH 1.5 and not greater than pH 3.5.

4. A method as described in claim 1 wherein the current is maintained in the range of 50 a.s.f. to 80 a.s.f. and the pH is not less than about pH 1.5 and not greater than pH 3.5.

5'. A new and improved insoluble anode nickel electroplating method for providing low anode current efliciencies and for preventing detrimental intergranular corrosion of the anode which comprises, establishing an all-sulfate nickel plating solution in contact with a cathode and an insoluble anode characterized by a composite structure comprised of a core of wrought foundation metal and a firmly adherent surface layer of electro deposited nickel, maintaining the anode current density such that it does not fall below about 40 a.s.f. and controlling the pH of said plating solution at a pH of not les than pH 1 and not greater than pH 4.5 while maintaining the temperature of said plating solution at a temperature of not less than about 120 F., whereby a relatively smooth cathode deposit of nickel is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,263,959 Swartley Apr. 23, 1918 2,275,194 Sizelove Mar. 3, 1942 2,365,356 Pilling et a1 Dec. 19, 1944 OTHER REFERENCES Hammond: Transactions American Electrochemical Society, volume 30 (1916), pages 106-111. 

1. A NEW AND IMPROVED INSOLUBLE ANODE NICKEL ELECTROPLATING METHOD FOR PROVIDING LOW ANODE CURRENT EFFICIENCIES OF NOT GREATER THAN ABOUT 6% AND FOR PREVENTING DETRIMENTAL INTERGRANULAR CORROSION OF THE ANODE WHICH COMPRISES, ESTABLISHING AN ALL-SULFATE NICKEL PLATING SOLUTION IN CONTACT WITH A CATHODE AND AN INSOLUBLE ANODE CHARACTERIZED BY A COMPOSITE STRUCTURE COMPRISED OF A CORE OF WROUGHT NICKEL AND A FIRMLY ADHERENT SURFACE LAYER OF ELECTRODEPOSITED NICKEL, MAINTAINING THE ANODE CURRENT DENSITY SUCH THAT IT DOES NOT FALL BELOW ABOUT 30 A.S.F., AND CONTROLLING THE PH OF SAID PLATING SOLUTION AT A PH OF NOT LESS THAN ABOUT 1 AND NOT GREATER THAN ABOUT 4.5 WHILE MAINTAINING THE TEMPERATURE OF SAID PLATING SOLUTION AT A TEMPERATURE OF NOT LESS THAN ABOUT 120* F., WHEREBY A SMOOTH CATHODE DEPOSIT OF NICKEL IS OBTAINED. 